﻿//-----------------------------------------------------------------------
// <copyright company="www.3WayWebdesign.de">
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
// </copyright>
//
// <author>Michael Morbach</author>
// <email>Michael@3waywebdesign.de</email>
// <web>http://www.3waywebdesign.de</web>
//-----------------------------------------------------------------------

using System;
using System.Globalization;
using System.Windows.Data;

namespace Tww.Wpf.Controls.Converters
{
    /// <summary>
    /// Converts the value from true to false and false to true.
    /// </summary>
    public sealed class IsNullOrEmptyConverter : IValueConverter
    {
        #region  - Felder (privat) -

        private static IsNullOrEmptyConverter _instance;

        #endregion

        #region  - Konstruktoren -

        /// <summary>
        /// Explicit static constructor to tell C# compiler not to mark type as beforefieldinit
        /// </summary>
        static IsNullOrEmptyConverter()
        {
        }

        #endregion

        #region  - Konstruktoren -

        private IsNullOrEmptyConverter()
        {
        }

        #endregion

        #region  - Indexer und Eigenschaften (öffentlich) -

        public static IsNullOrEmptyConverter Instance
        {
            get { return _instance ?? (_instance = new IsNullOrEmptyConverter()); }
        }

        #endregion

        #region  - IValueConverter Members -

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value == null || (value is string && string.IsNullOrEmpty((string)value));
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Binding.DoNothing;
        }

        #endregion
    }
}